1. Field of the Invention
The present invention relates generally to monomers and polymers derived from agricultural feedstocks, and more particularly to methods for the production of monomers from renewable agricultural resources such as feedstocks, for example canola, flax and tallow, and polymers, in particular polyurethanes, produced from such monomers.
2. Brief Description of the Related Art
With the realization that oil resources are becoming increasingly hard to find and expensive to produce, many industries that use oil as their source of raw material are looking to other sources, preferably renewable sources. At present, the production of plastics is still mainly based on the use of oil resources and a very large subgroup (about 10%) of the plastics industry includes the production of various polyurethanes (American Plastics Council (http://www.americanplasticscouncil.org). Accessed Apr. 10, 2005).
The preparation of polymers from renewable sources is of significant economic and scientific importance. As an inexpensive, readily available renewable resource, attention has been paid to renewable resources such as vegetable oils which are abundant and varied as a source for polymeric materials. Since they are composed of triacylglycerols containing predominantly unsaturated fatty acids, native North American vegetable oils are chemically relatively unreactive. But other functional groups such as hydroxyl, epoxy, or carboxyl groups can be introduced at the positions of double bonds (Petrovic, Z. R., Guo, A.; Zhang, W., J Polymer Sci A Polym. Chem 38: 4602 (2000) to produce reactive raw materials, which have been utilized in producing valuable polymeric materials. Present methods of using vegetable oils in polyurethane production require alcohol functionality to form what are widely referred to as polyols.
Vegetable oils are predominantly made up of triacylglycerol molecules and have complex structures (O'Brien, R. D., Fats and Oils: Formulating and Processing for Applications, CRC press, Boca Raton, Fla., pp 16-17, 2004). Triacylglycerol molecules are constituted by three fatty acids (varying from 14 to 22 carbons each in length for North American seed oils) and connected to a glycerol backbone through ester linkages. The fatty acids constituting most common North American seed oils have 0 to 3 double bonds which provide the sites of reactivity to convert the triacylglycerol structure of the vegetable oil into a triacylglycerol polyol, the raw material suitable for polymer production. Some triacylglycerol oils such as castor and vernonia oils develop specialized functional hydroxyl or epoxy groups and the others (such as canola, flax or linseed oils) have a double-bond functionality which provides reaction sites which enables them to be processed into high-value biochemicals for various industries (Pryde, E. H., L. H. Privcen, and K. D. Mukherjee (Eds.), New Sources of Fats and Oils, American Oil Chemists Society, Champaign, Ill., 1981).
In polymer applications, certain grades of vegetable oils and their derivatives, such as polyol products, have been industrially explored as an alternative feedstock to produce additives or components for composites or polymers with definite advantages when compared with fossil and mineral raw materials (Pryde, E. H., L. H. Privcen, and K. D. Mukherjee (Eds.), New Sources of Fats and Oils, American Oil Chemists Society, Champaign, Ill., 1981).
In the polymer field (which includes materials such as poly vinyl chloride (PVC) and polyurethane, and the like), plant oils based materials with varying physical, mechanical and thermal properties have been produced (Salunkhe, D. K., J. K. Chavan, R. N. Adsule, S. S. Kadam, in World Oilseeds: Chemistry, Technology, and Utilization; Van Nostrand Reinhold, New York, pp 87-89, 1992; John, J., M. Bhattacharya and R. B. Turner, Characterization of polyurethane foams from soybean oil, J. Appl. Polym. Sci. 86, 3097-3107 (2002); Khot, S. N., J. J. Lascala, E. Can, S. S. Morye, G. I. Williams, G. R. Palmese, S. H. kusefoglu and R. P. Wool, Development and application of triglyceride-based polymers and composites, ibid. 82: 703-723 (2001)), but much more needs to be done to widen the pool of biochemical feedstock, enhance the yields, optimize the processes, and broaden the products.
Polyurethanes which have a wide range of applications (elastomers, rigid set resins, flexible slab, and foams) are traditionally industrially produced by reacting petroleum based polyols with isocyanates (Szycher, M., Szycher's Handbook of polyurethanes, CRC Press, Boca Raton, Fla., 1999). In recent years, naturally functionalized triacylglycerol oils (Barrett, L. W., L. H. Sperling, C. J. Murphy, Naturally functionalised triglyceride oils in interpenetrating polymer networks. J. Am. Oil Chem. Soc. 70: 523-534 (1993); Carlson K. D. and S. P. Chang, Chemical epoxidation of a natural unsaturated epoxy seed oil from Vernonia galamensis and a look at epoxy oil markets., ibid. 62: 934-939. (1985)) as well as vegetable oil polyols have attracted attention for making a multitude of plastic products including various polyurethanes (PUs) (Khoe, T. H., F. H. Otey, and E. N. Frankel, Rigid urethane foams from hydroxymethylated linseed oil and polyol esters, ibid. 49: 615-618 (1972); Lyon, C. K., V. H. Garret and E. N. Frankel, Rigid urethane foams from hydroxymethylated castor oil, safflower oil, oleic safflower oil, and polyol esters of castor acids., ibid. 51: 331-334 (1974); Guo, A., Y. Cho and Z. S. Petrovic, Structure and properties of halogenated and nonhalogenated soy-based polyols., J. Polym. Sci: Part A: Polym. Chem. 38: 3900-3910 (2000); Guo, A., D. Demydov, W. Zhang and Z.S. Petrovic, Polyols and polyurethanes from hydroformylation of soybean oil., J. Polym. & Environ. 10: 49-52 (2002); Hu, Y. H., Y. Gao, D. N. Wang, C. P. Hu, S. Zu. L. Vanoverloop and D. Randall, Rigid polyurethane foam prepared from a rape seed oil based polyol., J. Appl. Poly. Sci., 84: 591-597 (2002); Dwan'Isa, J.-P. Latere, A. K. Mohanty, M. Misra, L. T. Drzal and M. Kazemizadeh, Novel Biobased Polyurethanes Synthesized from Soybean Phosphate Ester Polyols: Thermomechanical Properties Evaluations., J. Polym. & Environ. 11: 161-168 (2003)).
The alcohol functionality also can already be found in some natural oils such as castor oil (Saxena, P. K., S. R. Srinivasan, J. Hrouz, and M. Ilavsky, The Effect of Castor Oil on the Structure and Properties of Polyurethane Elastomers, J. Appl. Polym. Sci. 44: 1343-1347 (1992)).
Alternately research groups have sought to introduce alcohol functionality utilizing the reactivity of double bonds to hydroformylate (Lyon, C. K., V. H. Garret, and E. N. Fankel, Rigid Urethane Foams from Hydroxymethylated Castor-oil, Safflower Oil, Oleic Safflower Oil and Polyol Esters of Castor Acids, J. Am. Oil Chem. Soc. 51(8): 331-334 (1974)) or introduce epoxides that can later be opened in various ways (Hu, Y. H., Y. Gao, D. N. Wang, C. P. Hu, S. Zu, L. Vanoverloop, and D. Randall, Rigid Polyurethane Foam Prepared from a Rape Seed Oil Based Polyol, J. Appl. Polm. Sci. 84: 591-597 (2002)).
For example, Frankel and group (Khoe, T. H., F. H. Otey, and E. N. Frankel, Rigid urethane foams from hydroxymethylated linseed oil and polyol esters, J. Am. Oil. Chem. Soc. 49: 615-618 (1972); Lyon, C. K., V. H. Garret and E. N. Frankel, Rigid urethane foams from hydroxymethylated castor oil, safflower oil, oleic safflower oil and polyol esters of castor acids, Ibid. 51: 331-334 (1974)) have produced derivatives of castor, safflower, and flax oils with enhanced hydroxyl groups, and Petrovic and group (Guo, A., D. Demydov, W. Zhang, and Z. S. Petrovic, Polyols and polyurethanes from hydroformylation of soybean oil, J. Polym. & Environ. 10-49-52 (2002)) have produced soybean oil based polyols.
The second method involves epoxidation of unsaturated fatty acids followed by alcoholysis reactions to introduce hydroxyl functionality. Petrovic and his group have successfully used it to produce polyols from soybean oil (Guo, A., Y. Cho, and Z. S. Petrovic, Structure and properties of halogenated and nonhalogenated soy-based polyols, J. Polym. Sci. Part A: Polym. Chem. 38: 3900-3910 (2000)). Hu and coworkers (Hu, Y. H., Y. Gao, D. N. Wang, C. P. Hu, S. Zu, L. Vanoverloop and D. Randall, Rigid polyurethane foam prepared from a rape seed oil based polyol, J. Appl. Polym. Sci. 84: 591-597 (2002)) have used this reaction to produce polyols from canola oil. The above technologies yielded heterogeneous triacylglycerol polyols with hydroxyl functionality situated in the middle of the fatty acid chains, causing significant steric hindrance during crosslinking reactions in the production of polymers.
However, the polyols produced so far by the reported technologies have their hydroxyl groups located in the middle of the triacylglycerol fatty acid chains leaving pendant chains of the triacylglycerol (also known as dangling chains) unsupported, which significantly limits the rigidity of the resulting polyurethanes. Significant steric hindrance to crosslinking (especially by bulky aromatic diisocyanates) are introduced by the —OH groups being located in the middle of the fatty-acid moieties, leading to less than optimized cross-linking density. Moreover, these dangling chains which are imperfections in the final polymer network, do not support stress if the network is under load and act as plasticizers which reduce the polymer rigidity and increase its flexibility.
Ozonolysis was used to obtain polyols with aerminal primary hydroxyl groups and different functionalities from trilinolein, low-saturation canola oil, and soybean oil (Petrovic, Z. S., W. Zhang, and I. Javni, Structure and properties of polyurethanes prepared from triacylglycerol polyols by ozonolysis, Biomacromolecules, 6: 713-719 (2005). In this study, ozonation of the oils was carried out in methylene chloride/methanol at −30 to −40° C., and sodium borohydride was used as the reducing agent.
It has been shown that polyurethanes produced using vegetable oils present some excellent properties such as enhanced hydrolytic and thermal stability, as shown with soybean oil based PUs (Zlatanic, A., A. S. Petrovic and K. Dusek, Structure and Properties of Triolein-Based Polyurethane Networks., Biomacromolecules, 3: 1048-1056 (2002)).
In terms of other useful materials derived from feedstocks, wax esters consist of a fatty acid esterified to a fatty alcohol. A number of waxes are produced commercially in large amounts for use in cosmetics, lubricants, polishes, surface coatings, inks and many other applications.
In view of the above, there remains a need for novel methods for the production of monomers and polymers having terminal hydroxyl functional groups from renewable resources, such as feedstocks. In particular, the use of renewable feedstocks, such as vegetable oils including canola and flax, to produce monomers capable of producing high-quality polymers, such as polyurethane foams and elastomers, utilizing reactions which are easily and inexpensively performed at an industrial scale would be highly desirable. The development of novel methods of producing wax esters is also highly desirable.